linux-kernel - Re: [PATCH 03/32] timens: Introduce CLOCK

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Message-ID: <alpine.DEB.2.21.1902072225420.1645@nanos.tec.linutronix.de>
Date:   Thu, 7 Feb 2019 22:40:55 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dmitry Safonov <dima@...sta.com>
cc:     linux-kernel@...r.kernel.org, Andrei Vagin <avagin@...nvz.org>,
        Adrian Reber <adrian@...as.de>,
        Andrei Vagin <avagin@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Andy Tucker <agtucker@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jeff Dike <jdike@...toit.com>, Oleg Nesterov <oleg@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Shuah Khan <shuah@...nel.org>,
        containers@...ts.linux-foundation.org, criu@...nvz.org,
        linux-api@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 03/32] timens: Introduce CLOCK_MONOTONIC offsets

On Wed, 6 Feb 2019, Dmitry Safonov wrote:
>  #include "timekeeping.h"
>  #include "posix-timers.h"
> @@ -1041,6 +1042,9 @@ SYSCALL_DEFINE2(clock_gettime, const clockid_t, which_clock,
>  
>  	error = kc->clock_get(which_clock, &kernel_tp);
>  
> +	if (!error && kc->clock_timens_adjust)
> +		timens_clock_from_host(which_clock, &kernel_tp);

Why are you adding this conditional instead of sticking the offset
magic into the affected ->clock_get() implementations?

That spares you the switch() and the !offsets conditional.

> +static void clock_timens_fixup(int clockid, struct timespec64 *val, bool to_ns)
> +{
> +	struct timens_offsets *ns_offsets = current->nsproxy->time_ns->offsets;
> +	struct timespec64 *offsets = NULL;
> +
> +	if (!ns_offsets)
> +		return;
> +
> +	if (val->tv_sec == 0 && val->tv_nsec == 0)
> +		return;

I have no idea why 0/0 is special.

> +
> +	switch (clockid) {
> +	case CLOCK_MONOTONIC:
> +	case CLOCK_MONOTONIC_RAW:
> +	case CLOCK_MONOTONIC_COARSE:
> +		offsets = &ns_offsets->monotonic_time_offset;
> +		break;
> +	}
> +
> +	if (!offsets)
> +		return;
> +
> +	if (to_ns)
> +		*val = timespec64_add(*val, *offsets);
> +	else
> +		*val = timespec64_sub(*val, *offsets);
> +}
> +
> +void timens_clock_to_host(int clockid, struct timespec64 *val)

Does this really need to be an out of line call? If you stick this into the
clock_get() implementations then it boils down to:

static inline void timens_add_monotonic(struct timespec64 *ts)
{
	struct timens_offsets *ns_offsets = current->nsproxy->time_ns->offsets;

	if (ns_offsets)
		*ts = timespec64_add(*ts, ns_offsets->monotonic_time_offset);
}

and

static int posix_ktime_get_ts(clockid_t which_clock, struct timespec64 *tp)
{
        ktime_get_ts64(tp);
	timens_add_monotonic(tp);
        return 0;
}

Hmm?

Thanks,

	tglx